Show activity-path alert details in Waterline coordination alerts

Format the workflow `activity_path` health check facts into a rich
Waterline coordination alert detail string when the check warns.
Mirrors the existing `task_transport` activity-path detail pattern:
counts overdue activities (schedule-to-start, start-to-close,
schedule-to-close, or heartbeat deadline past due without enforcement),
worst-case overdue and retry ages, retry-backlog count, and the
highest attempt count, then surfaces them in the alert details so
operators can read the activity-path stuck/duplicate-risk state from
one alert without re-aggregating metrics.

The new check name is added by the workflow Composer package on
`durable-workflow/workflow` v2. The Waterline change is purely
additive: when the package version Waterline runs against does not
yet emit `activity_path`, the new match arm is unreached and existing
behaviour is unchanged. When it does emit `activity_path`, the
existing `coordinationAlerts` infrastructure already routes the check
into the Waterline UI, and this commit upgrades the alert from a
default summary to the rich activity-path detail string.

Author: durable-workflow-ops

app/Http/Controllers/V2HealthController.php

@@ -162,6 +162,7 @@ private function healthCheckAlertDetails(string $key, array $facts): ?string
     {
         return match ($key) {
             'task_transport' => $this->taskTransportAlertDetails($facts),
+            'activity_path' => $this->activityPathAlertDetails($facts),
             'routing_health' => $this->routingHealthAlertDetails($facts),
             'durable_resume_paths' => $this->durableResumePathAlertDetails($facts),
             'worker_compatibility' => $this->workerCompatibilityAlertDetails($facts),
@@ -221,6 +222,56 @@ private function taskTransportAlertDetails(array $facts): ?string
         return $parts !== [] ? ucfirst(implode('; ', $parts)).'.' : null;
     }
 
+    /**
+     * @param  array<string, mixed>  $facts
+     */
+    private function activityPathAlertDetails(array $facts): ?string
+    {
+        $timeoutOverdue = $this->integerValue($facts['timeout_overdue'] ?? 0);
+        $retrying = $this->integerValue($facts['retrying'] ?? 0);
+        $maxTimeoutOverdueAgeMs = $this->integerValue($facts['max_timeout_overdue_age_ms'] ?? 0);
+        $maxRetryingAgeMs = $this->integerValue($facts['max_retrying_age_ms'] ?? 0);
+        $maxAttemptCount = $this->integerValue($facts['max_attempt_count'] ?? 0);
+
+        $parts = [];
+
+        if ($timeoutOverdue > 0) {
+            $parts[] = sprintf(
+                '%d activity execution%s past a schedule-to-start, start-to-close, schedule-to-close, or heartbeat deadline without enforcement',
+                $timeoutOverdue,
+                $timeoutOverdue === 1 ? '' : 's',
+            );
+        }
+
+        if ($maxTimeoutOverdueAgeMs > 0) {
+            $parts[] = sprintf(
+                'worst-case overdue age %s',
+                $this->formatDurationMilliseconds($maxTimeoutOverdueAgeMs),
+            );
+        }
+
+        if ($retrying > 0) {
+            $parts[] = sprintf(
+                '%d activity execution%s in the retry backlog',
+                $retrying,
+                $retrying === 1 ? '' : 's',
+            );
+        }
+
+        if ($maxRetryingAgeMs > 0) {
+            $parts[] = sprintf(
+                'worst-case retry age %s',
+                $this->formatDurationMilliseconds($maxRetryingAgeMs),
+            );
+        }
+
+        if ($maxAttemptCount > 0) {
+            $parts[] = sprintf('highest attempt count %d', $maxAttemptCount);
+        }
+
+        return $parts !== [] ? ucfirst(implode('; ', $parts)).'.' : null;
+    }
+
     /**
      * @param  array<string, mixed>  $facts
      */